In recent years, radiographic imaging methods have been employed using a radiation image conversion panel employing photo-stimulable phosphors (hereinafter also denoted simply as stimulable phosphors).
It is essential that the stimulable phosphor layer of the radiation image conversion panel employed in a radiation image conversion method exhibits a high radiation absorption rate and a high light conversion rate, and also exhibits fine image graininess and excellent image sharpness.
Up to this point, many investigations have been made to enhance the sensitivity and the image quality by adjusting plural factors. Of these, as a means of improving radiation image sharpness, for example, many attempts have been made to enhance the sensitivity and the sharpness by controlling the shape of a stimulable phosphor which is formed.
One example used as a method in the trials was a stimulable phosphor layer comprising minute pseudo-columnar blocks deposited onto a support having an indented pattern surface, as described in Japanese Patent O.P.I. Publication 61-142497.
Further, the following trial methods are disclosed, for example; to use a radiation image conversion panel comprised of a stimulable phosphor layer which has been subjected to a shock treatment to develop cracks among the columnar blocks by depositing the stimulable phosphor on the support having a minute patterned surface as described in Japanese Patent O.P.I. Publication 61-142500; to use a radiation image conversion panel comprised of a stimulable phosphor layer formed on the support, on which surface cracks are generated from the surface side to be pseudo columnar as described in Japanese Patent O.P.I. Publication 62-39737; to provide a stimulable phosphor layer possessing voids which is formed on the support via vapor deposition, followed by being subjected to heat treatment which expands the voids into cracks, as described in Japanese Patent O.P.I. Publication 62-110200.
Disclosed is the radiation image conversion panel comprised of a stimulable phosphor layer, formed on the support via vapor deposition, which has elongated columnar crystals inclined to the line normal to the support as disclosed in Patent Document 1.
All of the trials to control the shape of the stimulable phosphor layer are to make the columnar crystals to prevent stimulated emission light (stimulated. luminescence) from diffusing in the lateral direction (emitted light reaching the surface of the support by repeated reflection at the boundary of the cracks or columnar crystals). Such prevention of lateral diffusion results in significantly enhanced sharpness of an image formed via stimulated luminescence.
Attempts have been made to improve image quality, specifically, sharpness in radiation image conversion panels having a stimulable phosphor layer which was formed via gas phase growth (deposition), as described in Patent Document 2. This was achieved by combining a phosphor layer comprised of columnar stimulable phosphor crystals described above with a low refractive layer, thereby preventing reflection or refraction at the interface between layers and resulting in enhanced image quality.
However, the requirements for improving the luminance and the sharpness are not satisfied by such a radiation image conversion panel having a stimulable phosphor layer formed via vapor deposition, and further improvement has been sought.    [Patent Document 1] Japanese Patent O.P.I. Publication 2-58000    [Patent Document 2] Japanese Patent O.P.I. Publication 1-131498